Telecommunications companies have bought more than 12,000 phone lines from Telecom, allowing them to offer competing services.
The Commerce Commission has reported the number for the first time.
Telecom was forced to sell its copper phone lines in May and they are proving popular.
But the Commerce Commission says it's difficult to measure how the unlocking of the copper-loop is affecting prices for services, as many providers are offering bundles of mobile, fixed line and broadband for one price.
The Commission monitors the telecommunications sector, compared to other OECD countries each quarter.
It says the ranking in the cost of fixed line has improved in the latest quarter, with the medium-user category coming 25th out of 30 countries.
But the commission says mobile phone plans that it benchmarks have not changed in price over the last 18 months, and still rank in the bottom quartile of the 30 countries surveyed.